Fuel Gauge - Reading Erratic
BULLETIN:00-02
GROUP:
20
DATE:
Jan 26, 2000
SUBJECT:
Fuel Gauge Reading Erratic
MODELS:
A6 Sedan with (All Wheel Drive) 1998
A6 Avant with (All Wheel Drive) 1999
Supersedes T.B. Group 20 Number 00-01 dated Jan 7, 2000
Superseded due to addition of revised sending unit Part Number along with new resistance values, and testing procedure for G169 sending unit.
Condition
Incorrect fuel reading on fuel gauge erratic.
May be caused by a malfunction in one of the three fuel tank sending units.
Service
The following overview of the fuel tank sending unit system is provided to gain a better understanding of how the system works.
Determination of fill volume
Within the complex geometry of the fuel tank, three fuel gauge tank sending units are used to signal the fuel level in the tank.
^ One or more of the senders for the fuel gauge operate, depending on how full the fuel tank is.
^ The three senders for the fuel gauge are connected in series. The individual resistances of the senders are added together to get a "total resistance".
^ A microprocessor in the instrument cluster, processes this data.
Electrical Circuit
-G- Sender for fuel gauge
-G1- Fuel gauge
-G169- Sender II for fuel gauge
-G237- Sender III for fuel gauge
Sending unit location
NOTE:
The lower sending units -G- and -G169- are accessible through openings under the rear bench seat cushion.
The upper sending unit -G237- is accessible through an opening in the luggage compartment.
Check fuel gauge sending units as follows:
Test Requirements
^ Observe all safety precautions (Group 20 of appropriate Engine Repair Manual).
^ Observe rules of cleanliness (Group 20 of appropriate Engine Repair Manual).
^ Always complete checking procedure (check all 3 sending units).
Fuel Tank, draining
- Remove fuse 28 from relay panel (left-row, fifth large fuse from top).
- Start and run engine until engine runs out of fuel (relieves pressure in fuel system).
- Switch ignition OFF
- Remove fuel supply hose from sending unit -G- and connect to VAG 1433A fuel cart or similar approved equipment.
- Connect VAG1348/3 remote switch with VAG1348/3-2 adapter to cavity for fuse 28.
- Connect test probe to Battery Positive Voltage (B+).
With remote switch connected:
- Operate switch and pump fuel into fuel cart until tank chambers for sending units -G237- and -G- are empty.
- Switch OFF VAG1348/3 remote switch and remove VAG1348/3-2 adapter from cavity for fuse 28.
- Remove test probe from Battery Positive Voltage (B+).
NOTE:
Chamber for sending unit -G169- will still be full of fuel remove fuel as follows:
- Reconnect fuel supply line to sending unit -G- with appropriate clamp.
- Reinstall fuse 28 in relay panel.
- Start and run engine for approx. 15 minutes.
NOTE:
Remaining fuel from chamber for sending unit -G169- will be siphoned into chamber for sending unit -G-.
- Switch ignition OFF.
- Remove fuse 28 from relay panel again.
- Start and run engine until engine runs out of fuel (relieves pressure in fuel system).
- Switch ignition OFF.
- Remove fuel supply hose from sending unit -G- and connect to fuel cart again.
- Reconnect VAG1348/3 remote switch with VAG1348/3-2 adapter to cavity for fuse 28.
- Connect test probe to Battery Positive Voltage (B+).
- Operate switch and pump fuel into fuel cart until tank chamber for sending unit -G- is empty.
- Switch OFF VAG1348/3 remote switch and remove VAG1348/3-2 adapter from cavity for fuse 28.
- Remove test probe from Battery Positive Voltage (B+).
- Reinstall fuse 28 in relay panel.
- Reconnect fuel supply line to sending unit -G- with appropriate clamp.
- Remove all three fuel tank sending units.
Fuel tank sending units, checking
- Using a Fluke 83 (or equivalent) and the VW 1594 test kit or the VAG 1594C test adapter, switch to the 400 ohm scale and check the resistance of each sending unit through the sweep range according to the tables shown.
CAUTION!
Part numbers are for reference only. Always check with your Parts Dept. for the latest parts information.
NOTE:
When checking each sending unit, position the unit as it would normally sit in the fuel tank.
- While observing the meter place your hand under the float and slowly raise the float arm (without applying any side pressure).
- Meter should show a steady rise in resistance without any open circuit (minor fluctuations in resistance may be noted).
- Prior to testing the -G169- sending unit, install a jumper wire between two terminals to complete circuit, then read resistance value.
If specified values are obtained on all three sending units:
- Reinstall sending units using NEW seals (and clamps as necessary).
- Check fuel gauge in instrument cluster and wiring from sending units to cluster.
If specified values are not obtained on any one sending unit:
- All three sending units must be replaced. DO NOT intermix old sending units with new sending units.
New sending units, checking
Prior to installing new sending unit:
- Raise and lower the float arm several times.
- Clean the sweep area on resistor board using a solvent based electronic cleaner which is safe on plastics and leaves no residue, such as Part No: ZVW 805 001 or equivalent (one can will clean many sending units).
NOTE:
Remember to install jumper wire prior to testing -G169- sending unit.
CAUTION!
DO NOT use any harsh cleaners such as carburetor cleaners.
Always read and follow precautions listed on cleaner container.
NOTE:
Any sending unit which does not meet specifications should not be used.
- Install new sending units using NEW seals (and clamps as necessary).
Fuel gauge, checking after sending unit installation
- Switch ignition ON.
- After procedure is performed, check and erase any stored DTC's using VAG 1551 Scan Tool.
- Remove VAG 1551 Scan Tool.
^ Fuel gauge (should read empty).
- Switch ignition OFF.
- Fill fuel tank fully.
- Switch ignition ON.
^ Fuel gauge (should read full).
- Switch ignition OFF.
- Drain fuel tank again using previously described procedure.
- Switch ignition ON.
- Check fuel gauge again (should read empty).
- Switch ignition OFF.
- Fill fuel tank fully.
- Switch ignition ON.
- Check fuel gauge again (should read full).
When procedure applies to vehicles within the New Vehicle Limited Warranty, use the following:
Part Identifier: 2015
Labor Operation: 2015711 345 TU